Period 3 Oxides:

Question 1

Describe the reaction between sodium and water

Answer 1

• vigorous reaction with cold water
• forms NaOH and H2
• fizzing Molten ball

Question 2

Reaction of magnesium with water and the steam:

Answer 2

Water : slow, and forms an insoluble Mg(OH)2 ppt layer and H2
Steam: forms MgO instead and H2

Question 3

How is SO3 formed from SO2?

Answer 3

Reacts with oxygen and a vanadium catalyst

Question 4

Describe the trend in melting points in period 3 oxides?

Answer 4

• decreases across the group with the exception of Na2O has the 4th highest melting point ahead of only the simple covalent compounds

Question 5

What are the 3 different structures formed in period 3 oxides?

Answer 5

• ionic lattices
• giant covalent compounds
• simple covalent compounds

Question 6

Why do giant ionic lattices have high melting points?

Answer 6

• strong forces of attraction between each oppositely charged ion

Question 7

What period 3 oxide forms a macro molecular structure:

Answer 7

SiO2

Question 8

What is the molecular formula of the oxide formed when phosphorus reacts with O2?

Answer 8

P4O10

Question 9

What is the trend in reactivity with period 3 elements and their reactivity with O2?

Answer 9

The reactive metals (Na Mg) react vigorously
The Non-metals (P, S) react readily
The other (Si Al) react slowly

Question 10

Why does Na2O have a lower melting point than MgO

Answer 10

• Mg forms a 2+ ion so bonds more strongly

Question 11

Why does Al2O3 have a lower melting point than MgO?

Answer 11

• the 3+ Al ion charge distorts the oxygens electron cloud making the bonds partially covalent

Question 12

After reacting Na2O and MgO with water an alkali solution is formed, Why is NaOH a more alkali solution than Mg(OH)2?

Answer 12

Mg(OH)2 is less soluble in water

Question 13

Which period 3 oxides form alkaline, acidic or amphoteric solutions when added to water?

Answer 13

Na2O and MgO form basic solutions
Al2O3 forms an amphoteric solution
SiO2, P4O10, SO2 form acidic solutions

Question 14

Are the acids formed by reacting period 3 oxides and water strong or weak? And how do we know?

Answer 14

Strong

• P4O10 makes phosphoric acid
• SO2 makes sulphurous acid
• SO3 makes sulphuric acid

Question 15

Why is Na more reactive than Mg with water?

Answer 15

• sodium only loses 1 electron when reacting with water where as Mg needs to lose 2 electrons which requires more energy